In a dynamic rigid disk storage device, a rotating disk is employed to store information. Rigid disk storage devices typically include a frame to provide attachment points and orientation for other components, and a spindle motor mounted to the frame for rotating the disk. A read/write head is formed on a “head slider” for writing and reading data to and from the disk surface. The head slider is supported and properly oriented in relationship to the disk by a head suspension that provides both the force and compliance necessary for proper head slider operation. As the disk in the storage device rotates beneath the head slider and head suspension, the air above the disk also rotates, thus creating an air bearing which acts with an aerodynamic design of the head slider to create a lift force on the head slider. The lift force is counteracted by a spring force of the head suspension, thus positioning the head slider at a desired height and alignment above the disk that is referred to as the “fly height.”
Head suspensions for rigid disk drives include a load beam and a flexure. The load beam includes a mounting region at its proximal end for mounting the head suspension to an actuator of the disk drive, a rigid region, and a spring region between the mounting region and the rigid region for providing a spring force to counteract the aerodynamic lift force generated on the head slider during the drive operation as described above. The flexure typically includes a gimbal region having a slider-mounting surface where the head slider is mounted. The gimbal region is resiliently moveable with respect to the remainder of the flexure in response to the aerodynamic forces generated by the air bearing. The gimbal region permits the head slider to move in pitch and roll directions and to follow disk surface fluctuations.
In one type of head suspension, the flexure is formed as a separate piece having a load beam-mounting region that is rigidly mounted to the distal end of the load beam using conventional methods such as spot welds. Head suspensions of this type typically include a load point dimple formed in either the load beam or the gimbal region of the flexure. The load point dimple transfers portions of the load generated by the spring region of the load beam to the flexure, provides clearance between the flexure and the load beam, and serves as a point about which the head slider can gimbal in pitch and roll directions to follow fluctuations in the disk surface.
The actuator arm is coupled to an electromechanical actuator that operates within a negative feedback, closed-loop servo system. The actuator moves the data head or head slider radially over the disk surface for track seek operations and holds the transducer or read/write head directly over a track on the disk surface for track following operations.
The preferred method of attaching the head suspension to the actuator arm is swaging because of the speed and cleanliness of the swaging process. Swaging also provides a strong joint that resists microslip. The swaging process has been in use in rigid disk drives since the late 1960s for attaching head-suspension assemblies to actuator arms.
The design of the swage joint has been reduced in size to keep up with the miniaturization of disk drives. However, recent moves to disk-to-disk spacings of under two millimeters have presented a severe problem. Miniaturization of the swage plates is not satisfactory because the torque-out capability that the swaged system drops too low to be useful.
U.S. Pat. No. 5,717,545 (Brooks, et al.) discloses a swage boss design using axially extending lobes or flutes formed in the outer peripheral surface of the boss to increase torque-out resistance without increasing the pry-out force necessary to remove the head-suspension assembly from the actuator arm.
U.S. Pat. No. 6,003,755 (Hanrahan, et al.) teaches a base plate geometry with a swaging hole that is tapered so that the minimum diameter is located farther away from the flange than the maximum diameter. The tapered swaging hole provides that in tension, the swage force and plastic strain build up slowly so that there exists a strain hardened area between the contact zone and the flange by the time the swaging ball really begins to work, thus isolating the flange region and the lower region of the hub. In compression, the ball immediately builds plastic strain energy while the ball is far away from the flange and by the time the ball gets near the flange the barrel diameter has enlarged creating a less intense plastic flow thus reducing the plastic strain near the critical flange area.
What is needed is an innovative way to increase the torque-out capabilities of swaged connections.